Establishing positions of locating field detectors and path mapping in underground boring tool applications

ABSTRACT

Specific apparatus and associated methods are described for use in establishing the positions of locating field detectors and for path mapping within a region for the purpose of tracking and/or guiding the movement of an underground boring tool. In one aspect, an improvement is provided forming part of an arrangement for tracking the position and/or guiding the boring tool using an electromagnetic locating signal which is transmitted from the boring tool as the boring tool moves through the ground. At least two detectors are located at fixed positions within the region, each being operable in a transmit mode and in a receive mode such that each one of the detectors in the transmit mode is able to transmit a relative locating signal to the other detector for use in determining the relative position of one detector in relation to the other and such that both detectors receive the electromagnetic locating signal in the receive mode for use in determining the position of the boring tool within the region. Provisions are also described for extending drilling range by using additional detectors by moving a limited number of detectors. In another aspect, a system is provided including at least two above ground detectors for sensing the locating signal. The detectors are located at initial positions in the region. Electromagnetic data is generated by the detectors with the boring tool at multiple positions to generate electromagnetic data which is used to identify the positions of the detectors. A selected flux pathline steering technique is introduced.

RELATED APPLICATION

The present application is a continuation application of copending priorapplication Ser. No. 10/694,926, filed on Oct. 27, 2003; which is adivisional application of prior application Ser. No. 10/353,718, filedon Jan. 28, 2003 and issued as U.S. Pat. No. 6,668,944 on Dec. 30, 2003;which is a continuation of application Ser. No. 10/039,971, filed onOct. 25, 2001, and issued as U.S. Pat. No. 6,536,538B1 on Mar. 25, 2003;which is a continuation of application Ser. No. 09/845,238, filed onApr. 30, 2001 and issued as U.S. Pat. No. 6,364,035 on Apr. 2, 2002;which is a continuation of application Ser. No. 09/324,221, filed onJun. 1, 1999 and issued as U.S. Pat. No. 6,250,402 on Jun. 26, 2001;which is a continuation-in-part of application Ser. No. 08/835,834,filed on Apr. 16, 1997 and issued as U.S. Pat. No. 6,035,951 on Mar. 14,2000; the disclosures of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates generally to horizontal boring toolapplications and, more particularly, to systems, arrangements andmethods for establishing positions of locating field detectors and forpath mapping within a region for the purpose of tracking the position ofand/or guiding an underground boring tool which emits a locating fieldas it later progresses through the region during drilling operations. Aselected flux pathline steering technique is also introduced.

It should be appreciated that prior art systems for use in locating anunderground boring tool primarily employ walk-over locator arrangementsas disclosed, for example, in U.S. Pat. No. 5,337,002 which is assignedcommonly with the present application. Inasmuch as Applicant is unawareof any prior art systems utilizing locating field detectors in themanner described in the parent of the instant application, the presentapplication represents an advance which is particularly well suited foruse with the systems and arrangements disclosed in the parent case.While the detector locating techniques disclosed in the parent caseremain effective, the arrangements and method disclosed below areremarkably convenient and highly effective for their intended purpose,as will be seen.

SUMMARY OF THE INVENTION

As will be described in more detail hereinafter, there are disclosedherein arrangements, specific apparatus and associated methods for usein establishing the positions of locating field detectors and for pathmapping within a region for the purpose of tracking and/or guiding themovement of an underground boring tool.

In one aspect of the invention, an improvement is provided forming partof an arrangement for tracking the position and/or guiding the boringtool using an electromagnetic locating signal which is transmitted fromthe boring tool as the boring tool moves through the ground, theimprovement comprising at least two detectors located at fixed positionswithin the region, each being operable in a transmit mode and in areceive mode such that each one of the detectors in the transmit mode isable to transmit a relative locating signal to the other detector foruse in determining the relative position of one detector in relation tothe other and such that both detectors receive the electromagneticlocating signal in the receive mode for use in determining the positionof the boring tool within the region.

In another aspect of the invention, at least two detectors initiallyreceive the electromagnetic locating signal with the boring tool at afirst position to produce a first subset of electromagnetic data andthen the detectors receive the electromagnetic locating signal with theboring tool at a second position to produce a second subset ofelectromagnetic data. Thereafter, processing means combines the firstand second subsets of electromagnetic data to produce an overall set ofelectromagnetic data for use, along with the established relativeposition between the detectors in determining the absolute positions ofthe detectors in the region.

In still another aspect of the present invention, the detectors are ableto receive the electromagnetic locating signal in the receive modewithin a dipole range from the boring tool and are able to receive therelative locating signal within a relative range from a detector that isin the transmit mode. Additional detectors may be provided for purposesincluding extending drilling range or further improving system accuracy.Accordingly, at least one additional detector is positioned in theregion such that the additional detector may be out of the dipole rangefrom the boring tool, but within the relative range of at least a firstspecific one of the other detectors, the absolute position of which isknown in the region such that, with one of either the first specificdetector or the additional detector in transmit mode and the other oneof either the additional detector or the first specific detectorreceiving the relative locating signal, the relative position of theadditional detector is determinable in relation to the known position ofthe first specific detector so that, in conjunction with the knownposition of the first specific detector, the absolute position of theadditional receiver is established within the region.

In yet another aspect of the present invention, a system is providedincluding at least two above ground detectors for sensing the locatingsignal transmitted from the boring tool as part of an above groundarrangement, each of the detectors is configured for receiving thelocating signal. The detectors are located at initial positions in theregion within a dipole range of the electromagnetic locating signaltransmitted from the boring tool at a first, start position. Thelocating signal is received by the detectors with the boring tool firstat its start position to produce a first set of electromagnetic data.The boring tool is then moved to a second position. The electromagneticlocating signal is again received using the detectors with the boringtool at its second position to produce a second set of electromagneticdata. Absolute positions of the detectors within the region are thendetermined using certain information including the first and second setsof electromagnetic data in a predetermined way. In accordance with onefeature of the present invention, one or more additional subsets ofelectromagnetic data may be produced at one or more additional positionsof the boring tool. The additional subsets of electromagnetic data arethen used in determining the absolute positions of the detectors as partof the overall electromagnetic data. Each additional position of theboring tool shifts the balance from unknown values to known values by atleast one value. Accordingly, given a sufficient number of additionalpositions of the boring tool, the absolute positions of the detectorsmay be determined based solely on electromagnetic data.

In accordance with the aspect of the invention immediately above, thedrilling range of the system may be extended by moving the detectors tonew positions beyond their initial positions within the region.Electromagnetic data is generated with the boring tool at somesubsequent position which may be known since the boring tool may betracked up to this subsequent position with the detectors at theirinitial locations. The boring tool may then be moved to an additionalsubsequent position to generate further electromagnetic data. Theelectromagnetic data gathered at these subsequent positions of theboring tool may then be used in determining the new positions of thedetectors such that tracking and/or guiding of the boring tool may thenbe performed in an area which is out of range of the detectors at theirinitial positions.

In accordance with another feature of the present invention a mappingtool is provided as part of the system for tracking the position and/orguiding a boring tool in the ground as the boring tool moves along anunderground path which lies within a region. At least two above grounddetectors are provided, each detector being configured for receiving theelectromagnetic locating signal. With the boring tool at a startposition, the above ground detectors are located at initial fixedpositions within dipole range of the boring tool in an initial portionof the region for receiving the electromagnetic locating signal as theboring tool is later guided along an initial segment of the intendedpath within the dipole range of the boring tool. Without moving theboring tool from its start position, absolute positions of the detectorsare determined within the initial portion of the region. Thereafter, theinitial segment of the intended path is mapped through the initialportion of the region in a particular way using the detectors.Mapping/drilling range may be extended by moving the detectors in apredetermined way to new locations within an adjacent, new portion ofthe region including an adjacent, new segment of the intended path andestablishing absolute positions of the detectors within the adjacentportion of the region. Thereafter, without moving the boring tool fromits start position, the new segment of the intended path may be mappedin essentially the same manner as the initial segment through the newportion of the region through which the boring tool will later passafter having passed through the initial portion of the region. Mappingmay be further extended by repeatedly locating the detectors inadditional adjacent portions of the region and mapping the intended paththrough segments in these additional adjacent portions. Alternatively,each segment along the intended path may be mapped immediately prior todrilling. That is, each segment is mapped and drilled prior to mappingand drilling of the next segment along the intended path.

In one configuration, advantages of the present invention are providedin a system including a transceiver detector located at one fixedposition within the drilling region. The transceiver detector isconfigured for transmitting a relative locating signal in a setup modeand for receiving the electromagnetic locating signal from the boringtool in a tracking mode for use in establishing the position of theboring tool. At least one receiver detector is provided at another fixedposition within the region. The receiver detector is configured forreceiving the relative locating signal in the setup mode such that theposition of the receiver detector can be established relative to theposition of the transceiver detector based on the relative locatingsignal and for receiving the electromagnetic locating signal in thetracking mode for use in establishing the position of the boring toolconcurrent with a drilling operation.

In an additional aspect of the present invention, one above grounddetector is provided configured for receiving the locating signal at alocation within a dipole range of the locating signal transmitted fromthe boring tool at a first, start position. Before moving the boringtool to a second position, the locating signal is received at the firstposition to produce a first set of electromagnetic data. A second set ofelectromagnetic data is then produced with the boring tool at the secondposition. The absolute positions of the detector and the boring toolwithin the region are determined using certain information including thefirst and second sets of electromagnetic data in a predetermined way. Inone feature, the distance between the first and second positions ismeasured and used as at least part of the certain information.

In a further aspect of the present invention, an improvement is providedfor steering the boring tool using an electromagnetic locating signalwhich is transmitted from the boring tool as the boring tool movesthrough the ground. The improvement includes establishing a targetlocation towards which the boring tool is to be steered and, thereafter,selecting a flux pathline extending between the boring tool and thetarget location such that a constant flux ratio between a verticalcomponent of the locating field in a vertical direction and a horizontalcomponent of the locating field in a horizontal direction is presentalong the selected flux pathline. The boring tool is then guided alongthe selected flux pathline to the target location.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may be understood by reference to the followingdetailed description taken in conjunction with the drawings brieflydescribed below.

FIG. 1 is a diagrammatic elevational view of a horizontal boringoperation being performed in a region using one horizontal boring toolsystem manufactured in accordance with the present invention.

FIG. 2 is a diagrammatic elevational view of the system of FIG. 1 shownhere to illustrate one procedure for performing extended range drillingin accordance with the present invention.

FIG. 3 is a diagrammatic plan view of a horizontal boring operationbeing performed in a region using another horizontal boring tool systemmanufactured in accordance with the present invention showing a fourdetector network of detectors which receive a locating signal from aboring tool.

FIG. 4 is a diagrammatic plan view of the system of FIG. 3 shown here toillustrate the operation of the system using only two detectors.

FIG. 5 is a diagrammatic plan view of the system of FIG. 3 with sixdetectors positioned along an intended path of the boring tool shownhere to illustrate mapping the intended path using a highly advantageousmapping tool in accordance with the present invention.

FIG. 6 is a diagrammatic, perspective view of the mapping tool shown inFIG. 5 shown here to illustrate details of the configuration of themapping tool.

FIG. 7 is a diagrammatic plan view of a horizontal boring operationbeing performed in a region using still another horizontal boring toolsystem manufactured in accordance with the present invention showing asingle fixed location above ground detector which receives a locatingsignal from a boring tool.

FIG. 8 is a diagrammatic representation of a display for use in theselected flux pathline steering method of the present invention.

FIG. 9 is a diagrammatic view, in elevation, of a region of ground shownhere to illustrate the selected flux pathline steering method of thepresent invention.

FIG. 10 is a diagrammatic illustration of the x and z coordinate axesalso used in FIG. 9, shown here to illustrate the orientation of variousparameters.

FIG. 11 is a diagrammatic plan view of a horizontal boring operationbeing performed in which the boring tool passes beneath an above groundlocator, shown here to illustrate reversal of the locating field fluxlines.

DETAILED DESCRIPTION OF THE INVENTION

Attention is immediately directed to FIG. 1 which illustrates ahorizontal boring operation being performed using a boring/drillingsystem which is manufactured in accordance with the present inventionand generally indicated by the reference numeral 10. The drillingoperation is performed in a region of ground 12. The surface of theground is indicated by reference numeral 16. It is to be understood thatthe surface of the ground is shown as being substantially planar forillustrative purposes only and that the surface may include significantrelief features.

System 10 includes a drill rig 18 having a carriage 20 received formovement along the length of an opposing pair of rails 22 which are, inturn, mounted on a frame 24. A conventional arrangement (not shown) isprovided for moving carriage 20 along rails 22. A boring tool 26includes an asymmetric face 27 and is attached to a drill string 28. Itis to be understood that the relative dimensions have been exaggeratedas necessary in the figures for illustrative purposes. The boring toolis indicated at an initial, start point A and shown subsequently atcalibration points B and C for reasons to be described. The presentexample contemplates movement of the boring tool within a global xyzcoordinate system. For purposes of simplicity, in the present example,the x axis is coextensive with the ground and lies generally along anintended path of the boring tool, however, any other orientation atpoint A may be adopted within the constraints to be described. Theorigin of the global coordinate system is specified by reference numeral30 essentially at the point where the boring tool enters the ground.While a Cartesian coordinate system is used as the basis for the globalcoordinate systems employed by the various embodiments of the presentinvention which are disclosed herein, it is to be understood that thisterminology is used in the specification and claims for descriptivepurposes and that any suitable coordinate system may be used. As noted,the x axis extends forward along the surface of the ground. The y axisextends to the right when facing in the forward direction along the xaxis and the z axis is directed downwardly.

The drilling operation can be controlled by an operator (not shown) at acontrol console 44. It is noted that like reference numbers have beenused to refer to like components wherever possible with regard to theparent of the present application. Therefore, further descriptions ofconsole 44 and of other pertinent components will be limited hereinsince descriptions of these components may be found in the parentapplication. It should also be mentioned that dimensions in the variousfigures have been exaggerated for illustrative purposes. Severalcomponents of interest in console 44 include telemetry receiver ortransceiver 45, associated telemetry antenna 46 and a processor 50.

Boring tool 26 includes a mono-axial antenna such as a dipole antenna 54which is driven by a transmitter 56 so that a magnetic locating signal60 is emanated from antenna 54. Orientation sensors (not shown) provideangular orientation measurement that may include, for example, roll,pitch and yaw of the drill head. A temperature sensor (not shown) andany other desired drilling parameter sensors (not shown) may also beincluded. Power may be supplied to transmitter 56 from a set ofbatteries 62 via a power supply 64. For descriptive purposes, the boringtool locating signal apparatus may be referred to as a transmitter. Inaccordance with the present invention, first and second detectors 66 aand 66 b are positioned within the global coordinate system forreceiving locating signal 60 at positions P1 and P2, respectively.Detectors 66 are configured for measuring components of magneticlocating signal 60 along three receiving axes that may be orthogonalwith respect to one another. For descriptive purposes, the axes will beassumed to be orthogonal and are referred to herein as x_(r), y_(r) andz_(r) (not shown) defined within each detector. The receiving axes ofeach detector may be defined by an antenna structure 67 such as, forexample, the highly advantageous structure disclosed in copending U.S.application Ser. No. 08/968,636, which is incorporated herein byreference. It should also be noted that the antenna cluster receivingaxes are not necessarily aligned with the x, y and z axes of the globalcoordinate system. Magnetic information measured along the receivingaxes of either detector may be transmitted to operator console 44 in theform of a telemetry signal 68 which is transmitted from a telemetryantenna 69 and associated telemetry transceiver 70. Alternatively, theoperator console may be connected with the detectors using cabling (notshown). Telemetry signal 68 is picked up at the drill rig usingtelemetry antenna 46 and telemetry transceiver 45. Thereafter, thetelemetry information is provided to processor 50 such that the magneticfield information may be interpreted so as to determine the position ofthe boring tool in the global coordinate system or for use during thesetup procedures contemplated herein, as will be described. Moreover,magnetic field information may be preprocessed using a local processor(not shown) located within each detector 66 in order to reduce theamount of information which is transmitted from the detectors to theoperator console 44. Two-way communications between the detectors andthe drill rig and also between the detectors (neither of which is shown)may be accomplished through the use of suitable telemetry transceivers.In this manner, data can be polled and the telemetry transceivers in thedetectors may serve as repeaters.

Continuing to refer to FIG. 1, having generally described the componentsof system 10, it should be appreciated that the depicted layoutcomprises an initial drilling array. In this regard, the reader isreminded that the present invention is directed to establishing absolutepositions/coordinates of all of the components which make up the arraysuch that drilling may subsequently be performed. The absolute positionsof the detectors and the boring tool may, of course, be established in anumber of different ways in the prior art. For example, skilledpersonnel using surveying equipment may determine the absolutepositions. However, by performing survey measurements in such a manner,a significant amount of time and money may be expended. Accordingly, thepresent invention introduces a number of system configurations andassociated methods for establishing absolute positions of components ofthe drilling array which require little training or skill on behalf ofan operator of system 10. In fact, the system may be configured suchthat the setup procedures are essentially automatic, transparent to thesystem operator and require minimal operator skill, as will be seen.

Still referring to FIG. 1, the overall combination of established, knownabsolute positions (i.e., those of the boring tool and at least twodetectors) are required prior to drilling so as to enable effectivetracking of the boring tool will be referred to as the “absoluteconfiguration” of the drilling array hereinafter for purposes ofconvenience. A first setup procedure for establishing the drilling arrayabsolute configuration begins with boring tool 26 at position A. Asmentioned previously, the origin of the global coordinate system isassumed to be at the center of dipole antenna 56 which, of course, alsoidentifies the center of the radiation pattern of locating field 60.With the boring tool at position A, locating signal 60 is transmittedfrom the boring tool for receipt by detectors 66. Each detector producesa set of electromagnetic data by measuring the received signal strengthalong each axis of the antenna array housed by the respective detector.Therefore, the two detectors each produce three known values for a totalof six known electromagnetic values. In order to establish the absoluteconfiguration of the drilling array, the problem must be well posedmathematically. That is, there must be at least as many conditionalrelations or equations, as unknown values. The latter may include (1)the transmitted strength of magnetic locating signal 60, (2) an initialyaw (β_(A)) of dipole antenna 54 in the global coordinate system (whichis measured from the global x axis and is 0° in the present example,since dipole 54 is oriented along the x axis), (3) an initial pitchφ_(A) of dipole antenna 54, (4) the xyz location of detectors 66 a and66 b within the global coordinate system, (5) the orientation angles(pitch, roll and yaw) of the receiving axes of the detectors relative tothe global coordinate system and (6) the initial xyz location of theboring tool, for example, at origin 30 within the global coordinatesystem.

While a wide range of solutions may be formulated to deal with theforegoing list of unknown values, Applicants have made highlyadvantageous advances with regard to the systems and methods underdiscussion. It is initially noted that six known electromagnetic valuesare provided at position A or, for that matter, at any other position atwhich the boring tool is within range of the detectors. One of ordinaryskill in the art might readily dismiss this observation as being oflittle worth since six unknown values (x, y and z of each detector andpitch, roll and yaw of each detector) are, at the same time, contributedby each detector. That is, the balance of unknown versus known values isnot shifted by the detectors while values such as pitch of the boringtool and the signal strength of the locating signal remain unknown. Theunknowns outweigh the knowns associated with one detector such thatresolving the absolute configuration appears to be underdetermined and,thus, unsolvable as to absolute coordinates. However, the number ofunknown values associated with the boring tool at a particular locationbears further examination.

At each location of the boring tool in region 12, the associated unknownvalues are an xyz position, a pitch value and a yaw value. Because themagnetic field from the transmitter is symmetric, roll is not a variablein determining transmitter position. Thus, no more than five unknownvalues are contributed by the boring tool at any one position.Therefore, in accordance with the present invention, it is recognizedthat the number of unknown values in the overall problem of establishingthe absolute configuration can be reduced by performing locating fieldmeasurements with the detectors at fixed locations and with the boringtool at multiple locations since each location of the boring toolcontributes no more than five unknowns while contributing six knownelectromagnetic values from measurements by the two detectors.Remarkably, each additional location of the boring tool shifts thebalance from unknown values to known values by at least one for eachadditional position of the boring tool at which electromagneticmeasurements are made by the detectors. For this reason, given asufficient number of positions of the boring tool, the absoluteconfiguration of the drilling array can be determined based solely onelectromagnetic readings from the detectors. It should be appreciatedthat an implementation which relies solely on electromagneticmeasurements represents one end of a spectrum of possibleimplementations which advantageously utilize the unknown/known balanceshift disclosed above. Therefore, a number of specific implementationswill be described below. The described implementations are intended onlyas examples and are not considered as limiting the scope of theinvention as set forth in the claims.

Still referring to FIG. 1, in accordance with one implementation, it isdesired to establish the absolute configuration of the initial drillingarray by performing detector electromagnetic readings with the boringtool at start point A and then advancing the boring tool to point B.Table 1 lists unknown versus known values for this “two calibrationposition” implementation.

TABLE 1 KNOWN/UNKNOWN VALUES USING TWO BORING TOOL POSITIONS # of BTposns Descriptions of Unknowns # of unknowns Descriptions of Knowns # ofknowns 2 Detector Unknowns Detector Knowns xyz of Det 66a 3 Det 66a R,P, κ of Det 66a 3 magnetic values at posn A 3 xyz of Det 66b 3 magneticvalues at posn B 3 R, P, κ of Det 66b 3 Det 66b BT Unknowns magneticvalues at posn A 3 At Point A magnetic values at posn B 3 dipole signalstrength 1 P of BT 1 At Point B xyz of BT 3 P & Y of BT 3 TOTAL UNKNOWNS= 19 TOTAL KNOWNS = 12 Notes: BT = Boring Tool; R = Roll; P = Pitch; Y =yaw of BT; κ = yaw of detector; Det = Detector

The overall number of unknowns is 19 while the overall number of knownvalues is only 12. It should be noted that the number of unknowns withthe boring tool at point A is reduced by assuming that the origin of theglobal coordinate system is at the center of dipole 54 and that theinitial direction of the boring tool and dipole defines the direction ofthe x axis along the surface of the ground. As mentioned, the x axis isassumed to be in the plane of the surface of the ground for purposes ofsimplicity. Other, equally effective assumptions can be made, as one ofordinary skill in the art will appreciate in view of this disclosure. Itis apparent that a well posed mathematical problem cannot be formulatedbased only on electromagnetic readings of the locating field using theboring tool at only two initial calibration positions. Therefore, thedeficit of 7 known values must be supplied by other measurements or byother assumptions. Fortunately, certain information may readily bemeasured with sufficient accuracy to eliminate various unknowns. As afirst example, the drill rig may include an arrangement (not shown) formeasuring extension and/or retraction of drill string 28. If theextension of the drill string is measured from point A to point B andthis distance is assumed to be a straight path, three position equationscan be derived for point B representing three known values to increasethe number of known values to 15. Four additional unknown values mayreadily be eliminated by direct measurement comprising the tiltorientation of the detectors. That is, deviation of the x_(d) and y_(d)axes of each detector from the horizontal direction. With the additionof two tilt measurements per detector, there are 15 known values and 15unknown values, making the solution determined such that the absoluteconfiguration of the drilling array can be established. It is emphasizedthat the present example represents only one of many possibleimplementations for eliminating the required number of unknown values.For example, as an alternative, to tilt sensors, the detectors maysimply be leveled. Moreover, additional measured values can be used inorder to formulate a least square error solution in which the number ofknown values is greater than the number of unknown values so as toimprove the overall accuracy in determining the absolute configurationof the drilling array. For example, boring tool 26 may incorporate apitch sensor so as to convert the pitch of the boring tool from anunknown to a known value. Another value that can be eliminated from thelist of unknowns is dipole strength of the transmitter. Its value mayreadily be determined in a separate, above ground calibration procedureprior to drilling. The calibration procedure involves placing thetransmitter in the boring head at a known positional relationship to oneof the detectors and measuring the signal strength. The particularchoice in determining the absolute configuration depends on requiredspeed and accuracy, on the performance of processor 50 and also on thepersonal preference of the developer.

With reference now to Table 2 and FIG. 1, in accordance with anotherimplementation, it is desired to establish the absolute configuration ofthe initial drilling array by performing detector electromagneticreadings with the boring tool located at three initial/calibrationpoints. That is, at point C in addition to points A and B. Table 2 listsunknown versus known values for this three calibration positionimplementation.

TABLE 2 KNOWNS/UNKNOWNS USING THREE BORING TOOL POSITIONS # of BT posnsDescriptions of Unknowns # of unknowns Descriptions of Knowns # ofknowns 3 Detector Unknowns Detector Knowns xyz of Det 66a 3 Det 66a R,P, κ of Det 66a 3 magnetic values at posn A 3 xyz of Det 66b 3 magneticvalues at posn B 3 R, P, κ of Det 66b 3 magnetic values at posn C 3 BTUnknowns Det 66b At Point A magnetic values at posn A 3 dipole signalstrength 1 magnetic values at posn B 3 P of BT 1 magnetic values at posnC 3 At Point B xyz of BT 3 P & Y of BT 2 At Point C xyz of BT 3 P & Y ofBT 2 TOTAL UNKNOWNS = 24 TOTAL KNOWNS = 18 Notes: BT = Boring Tool; R =Roll; P = Pitch; Y = yaw of BT; κ = yaw of detector; Det = Detector

In this example, the overall number of unknown values is 24 while theoverall number of known values is 18. It should be observed that thedeficit in the number of known values as compared with known values is6, as compared with the example of Table 1 in which a deficit of 7unknown values is present. Therefore, as mentioned in the foregoingdiscussions, the number of known values is increased by at least onewith each additional calibration point of the boring tool at whichelectromagnetic readings are taken. The assumptions made in the exampleabove have also been adopted in this example whereby to eliminateunknowns. In particular, the origin of the global coordinate system isassumed as the center of dipole 54 and the initial direction of theboring tool (and, hence, dipole 54) define the direction of the x axisalong the surface of the ground, with the x axis in the plane of thesurface of the ground.

As in the example above, additional known values may be provided bycertain information such as, for example, position equations based uponthe measured extension of drill string 28. In this instance, threeposition equations may be provided for the boring tool at calibrationpoint B and another three position equations may be provided for theboring tool at calibration point C for a total of six additional knownvalues. With these six additional known values, the absoluteconfiguration of the drilling array can be determined. As onealternative, tilt sensors could be added to detectors whereby to supplyfour known values and a pitch sensor could be added to the boring toolwhereby to supply two known values (i.e., pitch at calibration point Band pitch at calibration point C) such that the tilt sensors incombination with the pitch sensors alone provide all six additionalrequired known values. In still other alternatives, the various measuredvalues, as described, may be combined with the electromagnetic knownvalues to establish a least square error solution.

Having established the absolute configuration of the initial drillingarray, the drilling operation may ensue wherein the boring tool isguided and/or tracked to some predetermined location which is withinrange of the detectors. That is, above a specified maximum range fromthe detectors, the latter will be unable to receive the locating signaltransmitted from the boring tool. Several highly advantageous approachesmay be utilized to extend the drilling range of the boring tool, as willbe described immediately hereinafter.

Turning now to FIG. 2, which also depicts system 10 and a proportionallylarger area of region 12, boring tool 26 is shown after having advancedto a point D. The range over which the locating signal is receivable forthe initial positions P1 and P2 of the detectors (shown in phantom atthese positions) is denoted as segment 1, corresponding to a firstportion of region 12. However, the boring tool is about to enter asecond portion of region 12 corresponding to a second segment (i.e.,segment 2) along the intended path of the boring tool. Within segment 2,the distance between the boring tool and either or both of detectors 66exceeds the maximum range of the dipole signal for any position of theboring tool along the intended path of segment 2. Because the boringtool has been tracked during its advance by system 10, the absolutecoordinates of point D are known. Moreover, the pitch and yaw of theboring tool are also known at point D. Therefore, prior to allowing theboring tool to advance along segment 2, detectors 1 and 2 are relocatedto new positions, respectively, within the second portion of region 12.

As a practical matter, for long drill runs, the P3 and P4 positionsshould be just within range of the boring tool at position D whereby tomaximize the length of segment 2. In this regard, the length of segment1 should be maximized in the same manner when drilling initially frompoint A (FIG. 2). It should be appreciated that the configuration of thesystem with the detectors at positions P3 and P4 while the boring toolis at point D is, in essence, identical to the problem described abovewith determining the locations of the detectors in their initialpositions, P1 and P2, since, in both instances, the location andorientation of the boring tool is known. Therefore, the proceduresemployed for the absolute configuration of the initial drilling arrayassociated with segment 1, as described above, are applicable in thesubsequent absolute configuration of the drilling array associated withsegment 2. For this reason, these descriptions will not be repeated andthe reader is referred to the foregoing discussions. It is to beunderstood that each time the boring tool is about to go out of range ofthe detectors, the procedure illustrated in FIG. 2 may be repeated suchthat drilling may proceed indefinitely based possibly, however, uponother constraints such as, for example, the range of telemetry signal 68between the detectors and the drill rig. It should also be appreciatedthat the use of the “goal post” arrangement of detectors 1 and 2 is notrequired. Alternatively, for example, a “leap frog” arrangement (notshown) of the detectors may just as readily be used in which thedetectors are arranged in a generally colinear manner along the intendedpath of the boring tool. Moreover, detectors may be positioned relativeto a segment in a relatively random imprecise manner so long as they arewithin range of boring tool 26. Therefore, the requisite skill of anoperator is minimal. As the transmitter moves beyond the range of one ofthe detectors, that detector could then be moved farther out. With threedetectors, the transmitter could always be kept within range of twodetectors while the third detector is being moved thereby avoiding theneed to stop the drilling operation. To that end, the present inventioncontemplates a configuration in which processor 50 may determine andsuggest, on the display at console 44 and/or on a portable unit to bedescribed below, suitable locations for the detectors and when thedetectors should be moved.

Referring to FIG. 3 in conjunction with FIG. 2, the foregoing discussiondescribes one way in which a drilling operation may be performed over anextended distance. That is, a distance which is beyond the capabilitiesof the detectors to receive the locating signals with the detectors atpositions within an initial drilling array. FIG. 3 illustrates anotherhighly effective system and associated method for performing extendeddrill runs, generally indicated by the reference numeral 100. System 100includes drill rig 18 positioned in region 12 for drilling along anintended path 102 using boring tool 26. Intended path 102 is shown asstraight for illustrative purposes. It is to be understood that anyintended path may be used in accordance with these teachings. Othercomponents of system 100 include detectors 1-4. The latter areessentially identical to detectors 66, described above, with theexception of one additional function. Specifically, detectors 1-4include the capability to transmit a relative locating or setup field103 using antenna array 67, as shown being transmitted by detector 1.This capability is permitted through the addition of a transceiver block104 connected to antenna array 67. Each detector may be placed into asetup transmit mode, for example, triggered by a telemetry signalreceived from console 44 for use in establishing the absoluteconfiguration, to be described at an appropriate point below, or, aswill be described immediately hereinafter, for determining the positionof one detector relative to a detector at a known position.

When a detector is in the setup transmit mode, its transceiver block 104causes antenna array 67 to transmit setup signal 103 which ischaracteristically a dipole field. In one embodiment, the relativelocating signal is transmitted sequentially from each axis of antennaarray 67. It should be noted that setup signal 103 is shown in FIG. 3 asbeing transmitted from the x axis of antenna array 67 in detector 1(assuming that the axes of antenna array 67 are oriented in parallel tothe corresponding axes of the global coordinate system, but this is nota requirement). For this example, it is assumed that the positioncoordinates and orientations of detectors 1 and 2 have already beenestablished. With detector 1 in setup transmit mode, all other detectorsare left in a receive mode such that they function in essentially thesame manner as aforedescribed detectors 66. For purposes of extendingthe drilling range of the boring tool, it is generally advantageous totransmit in the setup mode the setup signal from the farthest detectorfrom the boring tool having a known position. In this instance, it canbe seen that detector 1 is slightly farther from the boring tool thandetector 2.

Therefore, setup signal 103 is sequentially emanated from each of the x,y and z axes of antenna array 67 (with the x axis transmission beingillustrated) of detector 1 for recording by detectors whose positionsare to be determined such as detectors 3 and 4, in the present example.Assuming that a tilt sensor is present in each of the receivingdetectors, four unknown variables for each unknown detector positionwill be determined including xyz position coordinates and detector yawangle. Processing the three components of the magnetic field obtained,for example, from the x-component of the detector provides equations1-3, below, for the distance between the transmitting detector and areceiving detector, in the global Cartesian coordinate system:Δx=ƒ ₁(B _(xx) ,B _(yx) ,B _(zx),κ₂)  (1)Δy=ƒ ₂(B _(xx) ,B _(yx) ,B _(zx),κ₂)  (2)Δz=ƒ ₃(B _(xx) ,B _(yx) ,B _(zx),κ₂)  (3)

Here, the functions ƒ₁, ƒ₂, ƒ₃ may be derived by one having ordinaryskill in the art from the equations of a magnetic dipole inthree-dimensional space which are known in the art (see also, the parentof the present application, U.S. application Ser. No. 08/835,834 foradditional details). The variable κ₂ denotes the yaw angle of thereceiving detector and the magnetic field components measured by thatdetector are indicated as B_(xx),B_(yx) and B_(zx). The first subscriptof each of these components indicates the axis of antenna array 67 ofthe receiving detector being used while the second subscript (x)indicates that the measured field is transmitted by the x axis antennaof the transmitting detector. The total distance between the detectorsis given by the expression:D _(x)=√{square root over ((Δx)²+(Δy)²+(Δz)²)}{square root over((Δx)²+(Δy)²+(Δz)²)}{square root over ((Δx)²+(Δy)²+(Δz)²)}  (4)where D_(x) indicates that the distance is determined based ontransmission from the x axis of the transmitting detector.

An alternate method of calculating the total distance between detectorsemploys the complete set of detector field data. That is, nine valuesare measured by transmitting from each axis of antenna array 67 of onedetector and receiving using each axis of antenna array 67 of anotherdetector. Accordingly, an expression for the total distance is given as:

$\begin{matrix}{D = {K\left\lbrack \frac{m}{B_{T}} \right\rbrack}^{\frac{1}{3}}} & (5)\end{matrix}$where D is the total distance, K is a constant equal to the value 6⅙ orapproximately 1.348 and B_(T) is the magnitude of the total magneticfield, as defined below. The corresponding dipole strength of each ofthe transmitting antennas for antenna array 67 is denoted by the valuem. It should be noted that m is assumed to be equal for transmission ofsetup signal 103 from all three axes common to antenna array 67 of thetransmitting detector's transceiver. This assumption is accurate if theantennas are essentially identical and the antenna drive signals areidentical. The total magnetic field, based on all nine measured magneticvalues is:

$\begin{matrix}{B_{T} = \sqrt{B_{xx}^{2} + B_{yx}^{2} + B_{zx}^{2} + B_{xy}^{2} + B_{yy}^{2} + B_{zy}^{2} + B_{xz}^{2} + B_{yz}^{2} + B_{zz}^{2}}} & (6)\end{matrix}$where the subscripts of the nine magnetic values are designated inaccordance with the description above. Hence, the total magnetic fieldinduced at the receiving detector by all three transmitting antennas ofin the transmitting detector is B_(T). Note that B_(T) is the magnitudeof a vector sum since each transmitting antenna includes a differentmagnetic field.

An additional, fourth equation for the calculation of unknown detectorcoordinates and orientation is then obtained by requiring D=D_(x). Thecomputational problem is deterministic in the sense that the number ofequations is the same as the number of unknowns, but the solution canformally be obtained employing any of the least square solution methodsdescribed in the prior art. Assuming detector 1 is transmitting and theposition/yaw of detector 3 is to be determined, the translationalposition coordinates of detector 3 follow from:x ₃ =x ₁ +Δx  (7)y ₃ =y ₁ +Δy  (8)z ₃ =z ₁ +Δz  (9)where x₁, y₁ and z₁ are the known coordinates of detector 1 and x₃, y₃and z₃ are the coordinates for detector 3. Note that the positionincrements Δx, Δy and Δz depend on detector yaw angle, κ₂. There is onlyone particular value of κ₂ for detector 3 which will satisfy D_(x)=D,and this value, in general, must be determined by iteration.

In this regard, it should be appreciated that the use of the relativelocating signal establishes only a relative position and orientationbetween the detector in setup transmit mode and each receiving detector.However, if the absolute position of either one of a pair of detectorsin communication via the relative locating signal is known, the absoluteposition of the other detector can be determined based on the relativeposition information. As will be described hereinafter, the use ofrelative position information is highly advantageous, particularly withregard to providing for extended drill runs within the context of theoverall operation of system 100.

Having generally described the components of detectors 1-4 of system 100and the way in which setup signal 103 is used to establish the relativepositions between detectors once the initial drilling array has alreadybeen established, a description of the operation of the overall systemwill now be provided. Initially, it is noted that intended path 102 isdivided into segments 1-3 which are separated by vertically orienteddashed lines 106 a and 106 b. As in the preceding example, each segmentrepresents a range on the intended path over which the detectors arecapable of receiving locating signal 60 from boring tool 26. An initialdrilling array is shown in segment 1, with boring tool 26 at the originof the global coordinate system, as a first step in establishing theabsolute configuration of the initial drilling array. Using detectors 1and 2 in their receive mode, boring tool 26 transmits locating signal60.

TABLE 3 KNOWN/UNKNOWN VALUES USING TRANSCEIVER CONFIGURATION WITH BORINGTOOL AT A SINGLE INITIAL POSITION # of BT posns Descriptions of Unknowns# of unknowns Descriptions of Knowns # of knowns 1 Detector UnknownsDetector Knowns x and z of Det 1 2 Det 1 κ of Det 1 1 magnetic values atposn A′ 3 (R and P measured) y = y1, measured xyz of Det 2 3 Det 2 κ ofDet 2 1 magnetic values at posn B′ 3 (R and P measured) RelativePosition Data BT Unknowns Δx, Δy and Δz 3 At Initial Position dipolesignal strength 1 Y of BT (i.e., dipole 54) 1 TOTAL UNKNOWNS = 9 TOTALKNOWNS = 9 Notes: BT = Boring Tool; R = Roll; P = Pitch; Y = yaw of BT;κ = yaw of det; Det = Detector

Referring to Table 3 in conjunction with FIG. 3, the reader is remindedthat six unknown values are typically associated with each detector (xyzcoordinate location, pitch, roll, and yaw) for an initial total oftwelve unknown values. By specifying measurements of certaininformation, as summarized in Table 3, the absolute configuration of theinitial drilling array can be established (i.e., unknown values can bebalanced with known values) with the boring tool at its initiallocation. In particular, pitch of the boring tool is measured byincorporating a pitch sensor (not shown) in the boring tool and tiltsensors (not shown) are included in the detectors such that the pitchsensor eliminates one unknown value while the tilt sensors, incombination, eliminate four unknown values. One other unknown iseliminated by measuring the distance of detector 1 from the x axis,indicated as y1. Alternatively, detector 1 may be positioned directlyabove the x axis (not shown) so that y1=0. Another unknown valuecomprises the signal strength of locating signal 60. It should bementioned that signal strength may alternatively be eliminated as anunknown, for example, by following a separate calibration procedure, asdescribed previously. A final unknown value is taken as the yaw of theboring tool at its initial position, A, since determination of the yawof the dipole within the boring tool is generally difficult. Therefore,nine unknown values are present. By incorporating a magnetometer orother static magnetic field sensor (neither of which is shown) such as agiant magnetic resistor (GMR) in the boring tool, the yaw of the boringtool could be resolved in conjunction with the pitch and rollmeasurements, eliminating another unknown. The yaw measurement couldalso be used in other calculations such as the aforementionedcalibration.

Still referring to Table 3 and FIG. 3, by receiving the locating signal,six known values are obtained, however, this leaves a deficit of threevalues (assuming no yaw measurement) with regard to establishing theabsolute configuration of the initial drilling array. Therefore,relative position and orientation information is determined betweendetectors 1 and 2 by transmitting setup signal 103 from detector 1 todetector 2, as shown, or by transmitting from detector 2 to detector 1(not shown). Consistent with the aforedescribed technique forestablishing the relative positions between detectors, three additionalknown values are provided in the form of Δx, Δy and Δz equations.Therefore, in Table 3, nine overall unknown values are balanced by nineoverall known values such that the absolute configuration of the initialdrilling array associated with segment 1 is determinable.

Once the absolute configuration of the initial drilling array has beendetermined, drilling may proceed with the system tracking the progressof the boring tool along the intended path denoted as segment 1.However, either as drilling proceeds or prior to drilling, provisionsmay be made for drilling along segment 2 and segments thereafter. Tothat end, detectors 3 and 4 are positioned within the portion of region12 associated with segment 2. Detectors 3 and 4 are configuredessentially identically with detectors 1 and 2. Ideally, detectors 3 and4 should be just within range of locating signal 60 as the boring toolpasses from segment 1 to segment 2, and separated by a predetermineddistance from one another in a direction that is generally perpendicularto the intended path whereby to maximize the length of segment 2 alongthe intended path of the boring tool. Even though the “goal post”arrangement is advantageous in extending system range, it should beappreciated that detectors 3 and 4 may be positioned almost anywhere(even within the portion of region 12 associated with segment 1) so longas they are at least initially within range of the boring tool as itpasses to segment 2. Of course, the length of segment 2 will beinfluenced by any arrangement of detectors. In this regard, it is notedthat some minimum spacing between the detectors should be observed inorder to ensure tracking accuracy. This minimum separation is functionof the range and positional accuracy required. Maximum segment length ina goal post configuration is approximately twice the maximum range ofthe locating signal. A “leap frog” arrangement of the detectors is alsosuitable, as described above. If a leap frog configuration is adopted,optimum range can be achieved by positioning the detectors at intervalsalong the intended drilling path that are spaced apart by the maximumuseable range of locating signal 60. It is noted that a minimum signalto noise ratio can be used to determine maximum useable range.

Referring to FIG. 3, having established the absolute positions ofdetectors 1 and 2, the absolute positions of detectors 3 and 4 may bedetermined by establishing the position of these detectors relative tothe known positions of either or both of detector 1 and/or detector 2 inaccordance with the preceding description for determining detectorrelative positions, by sequentially transmitting (not shown) therelative locating signal, for example, from the three orthogonal axes ofthe antenna array of detector 3 and receiving the signal using theantenna array of detector 1, three position equations may be obtained.It should be appreciated, however, that with the inclusion of a tiltsensor in detector 3, four unknown values are present. These include thexyz position of detector 3 and its yaw. A fourth equation may beobtained by requiring D=D_(x) (see equations 8 and 9). Therefore, theabsolute position of detector 3 can be determined with the number ofknown values being equal to the number of unknown values. Additionalknown values can be obtained by also receiving the relative locatingsignal with detector 2. Thus, three additional position equations areavailable for a total number of six position equations. In this manner,a least square error solution can be employed for establishing theabsolute position of detector 3. Thereafter, the absolute position ofdetector 4 can be determined by transmitting the relative locatingsignal to one or more of detectors 1-3 in a manner consistent with theforegoing descriptions. Note that it is equally effective to transmitthe setup signal from any detector at a known position to detectors atunknown positions. For example, one or both of detectors 1 and 2 maytransmit (sequentially, of course) the setup signals for purposes ofdetermining the coordinates of detectors 3 and 4.

Continuing to refer to FIG. 3, it should be appreciated that thedrilling range over which system 100 may track boring tool 100 can beextended substantially indefinitely by placing additional detectorsrelative to subsequent segments of the intended drilling path. Forexample, detectors 5 and 6 (not shown) may be positioned for trackingalong segment 3 and their positions established using detectors 3 and 4.Thus, a network of detectors can be established to cover the entireintended drilling path. The drilling operation can then be performed inan uninterrupted manner, tracking the boring tool as it progresses alongthe entirety of the intended path. One limit as to the overall length ofthe intended path may reside in the maximum range of telemetry signal 68from detectors farthest away from the drill rig. However, the telemetryrange of present systems developed for directional drilling is alreadysignificant, on the order of one-half mile. Moreover, the telemetryrange may be extended by suitable means such as, for example, by usingthe telemetry transceivers in the detectors to relay signals or toincorporate separate telemetry repeaters (not shown) into the system.Further advantages of system 100 will be brought to light in conjunctionwith the discussion of a highly advantageous feature to be described atan appropriate point below. It should be appreciated that in theinstance where a number of detectors are at once distributed at unknownpositions along some length of an intended path, the described methodcan be applied repeatedly, determining detector positions by movingfarther and farther away from the drill rig as positions of detectorsfarther and farther from the drill rig are established, until theposition coordinates and yaw angles of all detectors are known.

Referring to FIGS. 2-3, it should be appreciated that the teachingsherein may be combined in an unlimited number of ways for purposes ofovercoming an overall number of unknown values in a particulardrilling/tracking scenario. For example, an alternative system mayemploy teachings from both systems disclosed above. That is, such analternative system may readily be produced in which electromagnetic datais obtained by detectors which receive locating signal 60 fromsuccessive spaced apart positions of the boring tool in accordance withthe technique described above with regard to system 10. This alternativesystem may, in combination with the features of system 10, utilize thedetector transceiver feature of system 100 to establish relativepositions between certain ones of the detector transceivers whereby tofurther eliminate unknown values. Therefore, this alternative systemrepresents one of many possible systems which are considered to bewithin the scope of the present invention.

Still discussing system 100 with reference now to FIG. 4, in onemodification, the required number of detectors may be limited to two.This modification may significantly reduce the overall cost of thesystem while still permitting boring tool tracking over an extendeddrilling path. In a two detector configuration, after establishing theabsolute configuration of the initial drilling array, drilling proceedswhile tracking the boring tool to point E using detectors 1 and 2 atpositions A′ and B′, respectively. At point E, the boring tool is withinrange (albeit, typically at its maximum range for locating signal 60) ofpositions A′-D′. Drilling stops at point E and either detector 1 or 2 ismoved into the portion of region 12 associated with segment 2 in thedirections indicated by arrows 110 and 112. For example, detector 1 ismoved from position A′ to position C′ while detector 2 initially remainsat position B′. It is important not to disturb detector 2 at positionB′, since its absolute coordinates and orientation are known there. Withdetector 1 at position C′, the setup signal (not shown) may betransmitted between the two detectors in accordance with the foregoingdescriptions to establish the absolute coordinates and orientation ofdetector 1 based upon the known position and orientation of detector 2.Thereafter, detector 2 is moved from position B′ to position D′. Becausethe absolute coordinates and orientation of detector 1 are now known,the relative locating signal may once again be transmitted between thetwo detectors so as to establish the absolute coordinates andorientation of detector 2. Having thus established the absolutecoordinates and orientations of both detectors within the portion ofregion 12 associated with segment 2, boring tool 26 may be tracked alongsegment 2 of intended path 102. Once the boring tool reaches segment 3,the detectors may be moved to the portion of region 12 associated withsegment 3 and their positions established in the same manner. Therefore,the length of intended path 102 is not limited by the use of twodetectors. As mentioned above, with regard to exceptionally long drillruns, the range of telemetry signal 68 to the drill may be extendedthrough appropriate provisions.

Still referring to FIG. 4, in the interest of further reducing the costof system 100 without significantly affecting its capabilities, itshould be mentioned that the system may be configured with one detectortransceiver unit and one detector receiver unit (not shown). That is, adetector receiver unit similar to detectors 66 used in system 10 may beused in place of one of the detector transceivers of the dual detectorconfiguration of system 100. In using a detector receiver/transceiverconfiguration, the procedure described above may be used with thedifference, of course, that the relative locating signal is alwaystransmitted from the detector transceiver unit to the detector receiverunit. Even then, as drilling is advanced from one segment to the next,either one of the detector transceiver unit or detector receiver unitmay first be moved to the portion of region 12 associated with segment2, since the relative position (and, hence, the absolute coordinates andorientation of the moved unit) between the detector receiver unit anddetector transceiver unit can be established in either instance by meansof the relative locating signal.

Attention is now directed to FIG. 5 for purposes of discussion of ahighly advantageous configuration and feature of previously describedsystem 100. The reader is reminded that system 100 utilizes a “network”of detectors incorporating detectors such that the entire intended pathof the boring tool can be tracked without the need for intermediatesteps in which detectors are relocated along the intended path. Thelatter is indicated by the reference number 180 and differs fromintended path 102 in FIG. 3 in the respect that segment 2 of path 180 iscurved in a way which avoids an obstacle such as, for example, a largeboulder 182. Detectors 5 and 6 have been included to illustrate coverageof the detector network all along the illustrated portion of intendedpath 180. The absolute coordinates and orientations of detectors 5 and 6are readily established in accordance with the foregoing procedures. Themanner in which intended path 180 is established will be describedimmediately hereinafter.

Turning to FIG. 6 in conjunction with FIG. 5, a mapping tool isgenerally indicated by the reference number 200. Mapping tool 200 isportable and includes a case 202 having a handle. A display panel 206 ispositioned for ease of viewing and a keyboard panel 208 is providedhaving a series of buttons 210 for entry of necessary data. Power isprovided by a battery 212. A telemetry antenna 214 is driven by atelemetry transmitter 216 for transmitting a telemetry setup signal 218to operator console 44 and processor 50 (FIG. 2) therein. Thesetelemetry components and associated signal make up a telemetry link 220.Further components of the mapping tool include a mapping dipole antenna222 which is driven by a mapping signal generator 224. Other componentsmay be included such as, for example, a magnetometer 226, a tilt sensor228 and a processing section 230. Mapping dipole 222 is configured alongwith mapping signal generator so as to transmit a fixed, known strengthmapping signal 240 having a characteristic dipole field which ismeasurable in the same manner as magnetic locating signal 60 (FIG. 2).

Still referring to FIGS. 5 and 6, attention is now directed to the wayin which mapping tool 200 is used as part of system 100. It should beappreciated that mapping tool 200 may be located using setup signal 240within region 12 in essentially the same manner as boring tool 26 islocated using previously described locating field 60. With system 100 ina mapping mode initiated from console 44 and having established thedetector network all along intended path 180, the entire intended pathmay be mapped by placing the mapping tool sequentially at a number ofpoints, indicated as F through R, along the path. At each point, setupsignal 240 is transmitted to detectors that are within range such thatthe absolute position of the mapping tool may be determined in region12. For example, assuming the absolute configuration of the detectornetwork has been determined, an operator (not shown) may initiallyposition mapping tool 200 at point F. Thereafter, the operator may pressone of buttons 210 on keypad 208 so as to initiate transmission ofmapping signal 240. Detectors 1 and 2 then measure the strength of setupsignal 240 from positions A′ and B′ and transmit this information by wayof telemetry signal 68 to processor 50 in console 44 at the drill rig.Processor 50 then determines the absolute position of the mapping tool.In segment 2, the intended path is defined so as to steer around boulder182. The mapping procedure is completed once a sufficient number ofpoints have been identified along intended path 180. It is noted thatthe points need not be entered in the exact sequence that they areencountered along the intended path. That is, processor 50 may be usedto construct the intended path, appropriately ordering the points andthen displaying the intended path to an operator. It is mentioned thatthe mapping tool may be configured to be held above the ground as thesetup signal is transmitted. In such a configuration, the mapping toolmay measure the distance of its position above the ground, for example,as described in U.S. Pat. No. 5,155,442 which describes the use of sucha configuration within a portable walk over locating unit. Moreover, anintended depth of the intended drilling path may be entered into thesystem such that processor 50 establishes appropriate z axis depths forthe intended path as described, for example, in the parent of thepresent application, U.S. Ser. No. 08/835,834. In this way, the intendedpath may readily be modified (not shown), for example, to pass beneathor above an in-ground obstacle such as, for example, boulder 182.Alternatively, the grade of the intended path may be specified betweenpoints in absolute elevation rather than depth below the surface.

Referring again to FIG. 4, having described the use of mapping tool 200in a six detector implementation of system 100, it should be appreciatedthat the mapping tool may be used in any configuration of detectors,having either receiver or transceiver capability, for purposes ofestablishing an intended path in part or in its entirety prior todrilling. That is, there is no requirement for a network of detectorswhich at once covers all of the segments along the intended path. Forinstance, the mapping tool may be used effectively in several differentprocedures with the dual detector implementation of system 10, as shownin FIG. 4. The mapping tool may be used in a first procedure, forexample, by (1) mapping the intended path through a particular segmentrelative to which detectors 1 and 2 are positioned for tracking theboring tool, (2) advancing the boring tool along that particular segmentto the next segment, (3) relocating the detectors relative to the nextsegment and then (4) advancing the boring tool through this next segmentto still another segment. This procedure has the advantage that thedetectors need be moved only once relative to a particular segment. Themapping tool may be used in a second procedure, for example, by mappingthe intended path through a particular segment relative to detectors 1and 2, as in the first procedure, but then relocating the detectors fortracking relative to the next segment without actually drilling throughthe first segment. This next segment is then mapped using the mappingtool. The detectors may then be relocated relative to still anothersegment which is then mapped, again prior to any drilling. Therefore,this second procedure may advantageously map the entire intended pathusing only two detectors (or, alternatively, one detector incorporatinga receiver and one detector incorporating a transceiver, as describedabove with regard to a lower cost implementation) prior to drilling.

Referring to FIG. 6, it should be appreciated that information measuredby mapping tool 200, for example, using magnetometer 226 or tilt sensor228 may be used in least square error solutions so as to further improveoverall accuracy of the mapped/intended path. The mapping tool may alsobe employed in other useful ways. For example, in order to reduceaccumulated errors, the mapping tool may be positioned at a knownlocation within region 12. Such a known position could be established,for example, based upon Global Positioning System (GPS) measurements orby a survey marker. The positions and orientations of detectors withinrange of the mapping tool may then be refined based on measurements ofmapping signal 240, as transmitted from the known position. Thereafter,positions and orientations of all detectors (irrespective of whethereach detector incorporates a transceiver or receiver) within a networkmay be refined based upon the refined locations of the detectors withinrange of the mapping tool. Alternatively, as opposed to using mappingtool 200 for this purpose, a detector may be placed at a known locationfor transmitting setup signal 103. The setup signal can then be measuredby detectors incorporating transceivers or receivers within range of thetransmitting detector at the known location for use in refining thepositions of the receiving detectors in a similar manner. The mappingtool could also include antenna structure 67 (FIG. 1). That is, the sameantenna structure as used in the detectors for transmitting and/orreceiving purposes to improve positional accuracy, computational ease orin for use in conjunction with other advantageous procedures. Themapping tool may also serve as a locator for tracking the boring tool asdescribed, for example, in U.S. Pat. No. 5,633,589 entitled Device andMethod for Locating an Inground Object and a Housing forming Part ofsaid Device, which is incorporated herein by reference.

Attention is now directed to FIG. 7 which illustrates a horizontalboring operation being performed using another boring/drilling systemwhich is manufactured in accordance with the present invention andgenerally indicated by the reference numeral 300. The drilling operationis again performed in region of ground 12.

System 300 includes drill rig 18 and boring tool 26 transmittinglocating signal 60. Unlike previously described systems 10 and 100,however, system 300 includes only one detector indicated as “Detector A”for receiving locating signal 60 at a position denoted coordinateshaving the subscript “A”. Detector A is configured in accordance withpreviously described detectors which at least include the capability toreceive locating signal 60 along three orthogonally arranged axes usingantenna arrangement 67. System 300 further includes an arrangement (notshown) for measuring extension of drill string 28 as described, forexample, in the parent of the present application. The boring tool isindicated at an initial, start point a and shown subsequently at point bfor reasons to be described. As above, the present example contemplatesmovement of the boring tool within a global xyz coordinate system. The xaxis is coextensive with the ground and lies generally along intendedpath 102 of the boring tool, however, any other orientation at point amay be adopted within the constraints to be described. The origin of theglobal coordinate system is specified as being at point a. The y axisextends to the right when facing in the forward direction along the xaxis and the z axis (not shown) is directed downwardly into the x,yplane of the figure. Therefore, detector A is offset from the x axis bya distance y_(A). To avoid measuring y_(A), the detector can be placedon the x-axis in which case y_(A) becomes zero. In the present example,tilt angles of detector A are assumed to be measured or known from whichpitch and roll angles of the detector are derived. For each of initiallocations of the boring tool i.e., at points a and b, transmitter pitchφ is measured using a pitch sensor (not shown) in boring tool 26 andthree orthogonal components of the magnetic flux at the detector aremeasured. As mentioned, the origin of the global coordinate system x,y,zis chosen to coincide with the location of the transmitter at point asuch that x_(a)=y_(a)=z_(a)=0. Furthermore, the drill string increment,Δl, between the initial positions at points a and b is measured.

TABLE 4 KNOWN/UNKNOWN VALUES USING SINGLE DETECTOR AND TWO BORING TOOLPOSITIONS # of BT posns Descriptions of Unknowns # of unknownsDescriptions of Knowns # of knowns 2 Detector A Unknowns Detector AKnowns x_(A), z_(A) 2 magnetic values at pt a 3 β_(A) 1 magnetic valuesat pt b 3 BT Unknowns Known re BT dipole signal strength 1 Δl from pointa to point b giving 3 3 At Point a position equations β_(a) of BT 1 AtPoint b x_(b), y_(b), z_(b) 3 β_(b) of BT 1 TOTAL UNKNOWNS = 9 TOTALKNOWNS = 9 Notes: BT = Boring Tool; β = Yaw of BT; Det = Detector

Referring to Table 4 in conjunction with FIG. 7, five unknowns areassociated with detector A (x_(A) and z_(A) coordinate locations andyaw) since y_(A) and tilt are known. With regard to the boring tool,unknowns include yaw angles at points a and b, the transmitter dipolesignal strength and the coordinates of point b (x_(b), y_(b) and z_(b)).Therefore, in this instance, nine unknowns must be determined in orderto determine the absolute drilling configuration of system 300. Itshould be appreciated that other unknowns can be eliminated oradditional known values or conditional relations may be introduced, asis the case with aforedescribed systems. For example, transmitter dipolestrength could be determined in a separate calibration procedure priorto beginning drilling. Furthermore, detector A yaw angle could beeliminated from the list of unknowns by measuring its value usingcommercially available devices such as a magnetometer. In addition, allthree position coordinates of detector A could be obtained usingstandard surveying equipment. Unknown variables are ultimately chosenbased on accuracy requirements and ease of use of the locating system.Moreover, different solutions can be formulated based on desiredaccuracy. For example, a least square error approach can be adopted.

Continuing to refer to FIG. 7 and Table 4, nine equations can beformulated including: (i) three dipole equations for the magnetic fluxintensities emitted from the transmitter in the boring tool at point a,as measured by detector A, (ii) three dipole equations for the magneticflux intensities emitted from the transmitter in the boring tool atpoint b, as measured by detector A and (iii) three drill stringpositional equations for establishing the coordinates of point b interms of global coordinates.

The dipole equations can be written as:

$\begin{matrix}{B_{x} = \frac{{3x_{t}^{2}} - r^{2}}{r^{5}}} & (10) \\{B_{y} = \frac{3x_{t}y_{t}}{r^{5}}} & (11) \\{{B_{z} = \frac{3x_{t}z_{t}}{r^{5}}},{and}} & (12) \\{r^{2} = {x_{t}^{2} + y_{t}^{2} + z_{t}^{2}}} & (13)\end{matrix}$where x_(t),y_(t),z_(t) (not shown) indicate a three-dimensionalcoordinate system with its origin at the center of the boring tooldipole transmitter and having x_(t) oriented in the direction of itsdipole axis. In this instance, it is noted that x_(t),y_(t),z_(t)coincide with the global coordinate system axis for purposes of clarity,however, this is not required. The variables B_(x),B_(y),B_(z) denotethe components of the magnetic flux in the x_(t),y_(t),z_(t) coordinatesystem. The flux components, in instances where x_(t),y_(t),z_(t) do notcoincide with the global coordinate system, are obtained from the fluxcomponents measured at the detector by transformations that account fordetector yaw, roll, pitch, and also transmitter yaw and pitch. Dipoleequations 10-13 can be applied for each transmitter position resultingin a set of 6 equations.

Equations based on measured extension of drill string 28 for the boringtool at point b may be written as:x _(b)=cos φ_(av) cos β_(av) Δl  (14)y _(b)=cos φ_(av) sin β_(av) Δl  (15)z _(b)=sin φ_(av)Δl  (16)where φ_(av) represents average pitch and β_(av) represents average yaw.The average pitch and yaw angles of the transmitter are used to improveaccuracy and are given by:

$\begin{matrix}{\phi_{av} = {\frac{1}{2}\left( {\phi_{a} + \phi_{b}} \right)}} & (17) \\{\beta_{av} = {\frac{1}{2}\left( {\beta_{a} + \beta_{b}} \right)}} & (18)\end{matrix}$where φ_(a) and φ_(b) are measured values of pitch while β_(a) and β_(b)are the values of yaw at points a and b, respectively. Several standardnumerical solution methods are available to solve for the unknownvariables. If solved for nine unknowns, the problem is deterministicsince nine equations are available. In this case, many developers usethe method of Newton or function iteration. A least square solutionmethod is preferred if solving for fewer than nine unknowns. In eitherinstance, all parameters and locations regarding the boring tool anddetector A are known with the completion of calculations such thatdrilling may proceed as the boring tool is tracked in its undergroundprogress using system 300 in accordance with the teachings of the parentof the present application.

Having described various techniques for determining drillingconfigurations with regard to initial positional relationships and withregard to extended drill runs, attention is now directed to a highlyadvantageous selected flux pathline steering procedure performed inaccordance with the present invention as will be described in detailaccompanied by various figures. The procedure employs a single aboveground detector for the measurement of three flux components induced bya transmitter inside a boring tool. The detector includes a three-axisantenna cluster/array which can form part of a stationary detector orwhich can form part of a walkover locator. The procedure, as described,allows left/right as well as up/down steering of the boring tool whichmay be performed simultaneously. In this regard, the disclosed selectedflux pathline method is substantially different and highly advantageousas compared with conventional homing as described, for example, in U.S.Pat. No. 4,881,083, at least for the reason that the present inventionallows steering to a target point which is not at the receiving antennacluster location. Furthermore, the method provides for prescribing apitch angle other than the one associated with the antenna installation.

Turning now to FIG. 8, steering commands may be displayed on aninstrumentation panel 320 at an appropriate above ground location suchas, for example, at the drill rig or on a portable locator configuredfor remotely guiding the boring tool (see copending U.S. ApplicationSer. No. 09/066,964, filed Apr. 27, 1998 entitled Boring Tool UsingRemote Locator). In the present example, the boring tool should besteered up and to the right by the operator of the system in accordancewith a steering indicator 322. That is, a pointer 324 on the steeringindicator shows the direction in which the boring tool should bedirected to return to a path that is established in a way which will bedescribed below. The position of the steering indicator on the displayis to be established by determined values of ΔY and ΔZ. When steeringindicator 322 is centered on cross-hairs 326, the boring tool is oncourse and no steering is required. The purpose of the steering methoddescribed below is to provide the values of parameters ΔY and ΔZ, asindicated in the figure. Steering commands, as reflected in FIG. 9,relating the sign of each parameter to steering direction are summarizedin Table 5.

TABLE 5 ΔY ΔZ Steer  0 — Left <0 — Right — <0 Up — >0 Down

Referring to FIG. 9, for purposes of clarity, a discussion will first beprovided with regard to up/down steering and, thereafter, a separatediscussion of left/right steering will be provided. It should beappreciated, however, that during operation of the system the up/downand left/right steering features operate simultaneously. Boring tool 26is diagrammatically shown in region 12 including its locating fieldtransmitter which transmits locating field 60 including flux lines 60 aand 60 b. An above ground detector 340 includes a three axis orthogonalantenna array (not shown). Detector 340 may comprise a portablewalk-over detector/locator or a fixed position detector. Now consideringup/down steering, boring tool 26 can either be steered to the center ofthe antenna array within detector 340 or to a target location t belowthe antenna array. The desired transmitter pitch at the target locationmay be specified and may be non-zero. FIG. 9 illustrates steeringtowards target location t, approached at a pitch angle δ, at a depthD_(t) below detector 340. Note that flux line 60 a extends from theboring tool transmitter to target location t and flux line 60 b extendsfrom the boring tool transmitter to the antenna array in detector 340.Thus, flux line 60 a represents the desired path or “pathline” of theboring tool transmitter towards the target. In essence, specifying apitch value at the target location serves to select a flux line havingthat pitch as the target pathline. Therefore, the overall method isreferred to as “selected flux pathline” steering at various pointsthroughout this disclosure. Up and down steering commands through ΔZmust be such that the transmitter stays on this target pathline and thepitch angle or orientation of the boring tool matches the pathline slopeof flux line 60 a. If these two conditions are met, the ratio of thecomponents of flux in the vertical and horizontal directions at thetarget location will be the same as the specified transmitter pitchslope at the target location t, i. e.,

$\begin{matrix}{\left( \frac{b_{z_{t}}}{b_{x_{t}}} \right)_{ideal} = {\tan\;\delta}} & (19)\end{matrix}$where b_(z) _(t) and b_(x) _(t) represent the flux components oflocating field 60 at target point 342 along z and x axis directions,respectively, and δ is the pathline slope angle. Any deviation of thetransmitter from the ideal target pathline will result in a differentratio of flux components at the target from which an up/down steeringcommand is derived using:

$\begin{matrix}{{\Delta\; Z} = {{\tan\;\delta} - \frac{b_{z_{t}}}{b_{x_{t}}}}} & (20)\end{matrix}$

Referring to FIGS. 9 and 10, with the transmitter in the illustratedposition, the antenna array is used to measure the components ofmagnetic flux b_(x) and b_(z) at detector 340 since an in-groundmeasurement at the target location is not generally possible. Hence, themeasured fluxes at the detector must be converted to the flux componentsb_(x) _(t) , b_(z) _(t) at the target location. The conversion isaccomplished by first calculating transmitter depth D and horizontaldistance s from the antenna cluster to the transmitter using equations21-26, as follows:

$\begin{matrix}{D = {r\;{\sin\left( {\alpha + \phi} \right)}}} & (21) \\{s = {r\;{\cos\left( {\alpha + \phi} \right)}}} & (22) \\{b_{x_{s}} = {{b_{x}\cos\;\phi} + {b_{z}\sin\;\phi}}} & (23) \\{b_{z_{s}} = {{{- b_{x}}\sin\;\phi} + {b_{z}\cos\;\phi}}} & (24) \\{\frac{1}{r^{3}} = {{- \frac{b_{x_{s}}}{4}} + \sqrt{{\frac{9}{16}b_{x_{s}}^{2}} + {\frac{1}{2}b_{z_{s}}^{2}}}}} & (25) \\{{\tan\;\alpha} = \frac{b_{z_{s}}}{\frac{1}{r^{3}} + b_{x_{s}}}} & (26)\end{matrix}$

Equations 21 through 26 are based on the known magnetic dipoleequations. b_(x) _(s) and b_(z) _(s) are defined by equations 23 and 24.FIG. 10 illustrates the variables φ, a and r in relation to the x and zaxes of the overall coordinate system. A second step in deriving thetarget flux components b_(x) _(t) and b_(z) _(t) from the measuredfluxes b_(x), b_(z) involves the calculation of fluxes induced by thetransmitter at a distance D−D_(t) (FIG. 9) above the transmitter. Thehorizontal distance between target and transmitter, s, is unchanged.Hence, the target position in terms of x_(s) and z_(s), where x_(s) isalong the axis of the boring tool transmitter and z_(s) is perpendicularthereto, becomes:x _(s)=(D−D _(t))sin φ+s cos φ  (27)z _(s)=(D−D _(t))cos φ−s sin φ  (28)

Application of the equations of a magnetic dipole provides the desiredflux components at the target using equations 29-33:

$\begin{matrix}{b_{x_{s}} = \frac{{3x_{s}^{2}} - r_{s}^{2}}{r_{s}^{5}}} & (29) \\{b_{z_{s}} = \frac{3x_{s}z_{s}}{r_{s}^{5}}} & (30) \\{r^{2} = {s^{2} + \left( {D - D_{t}} \right)^{2}}} & (31) \\{b_{x_{t}} = {{b_{x_{s}}\cos\;\phi} - {b_{z_{s}}\sin\;\phi}}} & (32) \\{b_{z_{t}} = {{b_{x_{s}}\sin\;\phi} + {b_{z_{s}}\cos\;\phi}}} & (33)\end{matrix}$where r is defined in terms of s and depth per equation 31. Once ΔZ hasbeen obtained, it may be used in the formulation of the display of FIG.8. It should be understood that detector 340 is not required to be levelin order to obtain the flux components b_(x),b_(y),b_(z). Instead,gravitational angles of the locator may be recorded together with three“off coordinate axis” flux components. The angles and off coordinateaxis measured values are then transformed to obtain b_(x),b_(y),b_(z)using the measured angular orientation of the locator with respect tothe ground surface.

It should be appreciated that the aforedescribed transformation of fluxcomponents is not required if the transmitter is steered towards thedetector (i.e., where the target is the detector). However, transmitterpitch at the target can still be specified so that the steering commandmay be written as:

$\begin{matrix}{{\Delta\; Z} = {{\tan\;\delta} - \frac{b_{z}}{b_{x}}}} & (33)\end{matrix}$

Referring to FIG. 9, with regard to left/right steering, the x axisantenna of the antenna array (not shown) within detector 340 is orientedpointing in the direction of the desired drill path. Hence, the desiredazimuth angle is zero and steering is accomplished by forcing thecomponent of magnetic flux b_(y) normal to the desired drill path tovanish. In view of this, the steering command for ΔY then becomes:

$\begin{matrix}{{\Delta\; Y} = \frac{b_{y}}{b_{x}}} & (34)\end{matrix}$However, it should be appreciated that left and right steering can bemodified to allow the specification of an arbitrary azimuth angle.

It should be mentioned that the described procedure allows effectivesteering over both long and short distances. Maximum steering range isprimarily limited by transmitter signal strength and environmentalnoise. The required minimum distance between locator and transmitterdepends on how well transmitter position and angular orientation matchthe ideal drill pathline and its slope. Steering effectiveness at closerange may also be limited by the physical characteristics of the drillpipe and soil conditions.

Referring to FIG. 11, boring tool transmitter 26 is shown passingbeneath detector 340 in the direction given by an arrow 342. In suchshort range situations where the target is below the detector, it shouldbe appreciated that the flux lines of locating field 60 will reverse indirection as illustrated by a flux line 60 c. Steering towards anytarget on or below the antenna array/detector is possible even thoughthe flux lines recorded by the locator reverse direction. Further inthis regard, it should be appreciated that the sign of flux componentscannot be readily measured. Only their absolute values and the sign oftheir ratios are normally available. Therefore any practical steeringtechnique requires sign conventions in addition to the approachdescribed above. One method of determining the signs ofb_(x),b_(y),b_(z) assumes b_(z) to be positive and the signs of b_(x)and b_(y) to be given by the signs of b_(x)/b_(z) and b_(y)/b_(x),respectively. Note that the sign of b_(x)/b_(z) changes when thedirection in which the locator/detector points is reversed. Hence,during steering, the locator/detector should always point in the samedirection. Moreover, a boring tool transmitter can only be steered tothe locator or a target directly underneath but cannot be steered alonga desired path beyond the target. As mentioned above, flux lines fromthe transmitter to the target having the prescribed pitch slope at thetarget are desired pathlines. These flux lines converge approaching thetarget but diverge leaving the target. Hence, steering is a stableprocess ahead of the target but becomes unstable behind the target wherethe flux lines diverge. While the above method calls for a three axisreceiver, the procedure may also be employed using a two axis receiver(not shown) where the target point is substantially in the plane definedby the orthogonal antennas and the drill path is substantially in thesame plane.

Inasmuch as the systems and associated methods disclosed herein may beprovided in a variety of different configurations, it should beunderstood that the present invention may be embodied in many otherspecific forms and the methods may be practiced in many different wayswithout departing from the spirit of scope of the invention. Therefore,the present examples and methods are to be considered as illustrativeand not restrictive, and the invention is not to be limited to thedetails given herein, but may be modified within the scope of theappended claims.

1. In a system for tracking the position of a boring tool in the groundas the boring tool moves along an underground path which lies within aregion, said boring tool including a transmitter for transmitting anelectromagnetic locating signal and said system including an aboveground arrangement for receiving the electromagnetic locating signal foruse in establishing the position of the boring tool, a methodcomprising: a) providing at least two above ground detectors as part ofsaid above ground arrangement, each of which is configured for receivingsaid locating signal; b) locating said detectors at initial positions insaid region within a dipole range of said electromagnetic locatingsignal transmitted from the boring tool at a first, start position; c)receiving said electromagnetic locating signal using said detectors withsaid boring tool first at said start position to produce a first set ofelectromagnetic data; d) moving the boring tool to a second position; e)receiving said electromagnetic locating signal using said detectors withsaid boring tool at said second position to produce a second set ofelectromagnetic data; and f) determining absolute positions of thedetectors within said region using information including said first andsecond sets of electromagnetic data in a predetermined way.
 2. Themethod according to claim 1 including measuring a tilt orientation ofeach detector, using a tilt sensor in each detector, such that the tiltorientation of each detector forms part of said certain information. 3.The method according to claim 1 including measuring a pitch angle of theboring tool, using a pitch sensor in the boring tool such that the pitchangle of the boring tool forms part of said certain information.
 4. Themethod according to claim 1 wherein the electromagnetic locating signalincludes a known signal strength which forms part of said certaininformation.
 5. The method according to claim 1 including measuring adistance between the first and second positions of the boring tool and,thereafter, using said distance as part of said information to improvean accuracy in determining the absolute positions of the detectors insaid region.
 6. The method according to claim 5 wherein said distance isused in a way which overdetermines the absolute receiver positions so asto permit the use of a least square error technique.
 7. The methodaccording to claim 1 including (i) measuring a tilt orientation of eachdetector, using a tilt sensor in each detector, such that the tiltorientation of each detector forms part of said certain information,(ii) measuring a pitch angle of the boring tool, using a pitch sensor inthe boring tool such that the pitch angle of the boring tool forms partof said certain information, and (iii) using a known signal strength ofthe electromagnetic locating signal as part of said certain information.8. The method according to claim 1 wherein receiving saidelectromagnetic locating signal in said predetermined way furtherincludes producing one or more additional subsets of saidelectromagnetic data at one or more additional positions of said boringtool, said additional subsets of electromagnetic data, thereafter, beingused in determining the absolute positions of the detectors as part ofthe overall electromagnetic data.
 9. The method according to claim 8wherein the determination of the absolute positions of said detectorsincludes an overall certain number of known values and an overallcertain number of unknown values and wherein measurements taken at saidsecond position and at each additional position of the boring toolcontribute at least one more additional known value to said overallcertain number of known values such that the number of overall certainnumber of known values can be increased relative to the overall numberof unknown values.
 10. The method according to claim 9 whereinmeasurements are taken at a number of positions such that the overallcertain number of known values is equal to or greater than the overallcertain number of unknown values so as to use only electromagnetic datain determining the absolute positions of said detectors.
 11. The methodaccording to claim 9 wherein the determination of the absolute positionsof said detectors includes using the additional known values in place ofat least portions of said certain information.
 12. The method accordingto claim 11 wherein each detector includes a tilt orientation andwherein the determination of the absolute positions of said detectorsincludes using the additional known values instead of using measuredvalues of tilt orientation for said detectors such that the tilt valuesform part of said certain number of unknown values.
 13. The methodaccording to claim 12 wherein said boring tool includes a pitchorientation and wherein the determination of the absolute positions ofsaid detectors includes using the additional known values instead ofusing a measured value of said pitch such that the pitch orientationforms part of said certain number of unknown values.
 14. The methodaccording to claim 13 wherein said electromagnetic locating signalincludes a signal strength and wherein the determination of the absolutepositions of said detectors includes using the additional known valuesinstead of using an assumed value of said signal strength such that thesignal strength forms part of said certain number of unknown values. 15.The method according to claim 1 wherein said detectors are able toreceive said electromagnetic locating signal within said dipole range ofsaid boring tool and wherein said method further comprises: f) afterestablishing the absolute positions and orientations of said detectorswithin said region with the detectors at said initial locations withinthe region, moving the boring tool to a third position such that bothdetectors remain within said dipole range of the boring tool; g)establishing the absolute position and orientation of the boring tool atsaid third position within said region using the detectors at theirinitial positions; h) moving said detectors to new positions in saidregion or providing additional detectors at said new positions withinthe particular range of said boring tool; i) receiving saidelectromagnetic locating signal using the detectors at the new positionswith said boring tool at said third position to produce a firstsubsequent set of electromagnetic data; j) moving the boring tool to afourth position; k) receiving said electromagnetic locating signal usingthe detectors at the new positions with said boring tool at said fourthposition to produce a second subsequent set of electromagnetic data; l)using a set of information including at least said first and secondsubsequent sets of electromagnetic data in a predetermined way todetermine absolute positions of the detectors at the new positionswithin said region.
 16. The method according to claim 15 wherein thedetectors at the new positions are farther from the start position ofthe boring tool than at their initial locations such that the boringtool is locatable for a distance beyond said particular range from thestart position of the boring tool.
 17. In a system for tracking theposition of a boring tool in the ground as the boring tool moves alongan underground path which lies within a region, said boring toolincluding a transmitter for transmitting an electromagnetic locatingsignal and said system including an above ground arrangement forreceiving the electromagnetic locating signal, a method comprising: a)providing at least two above ground detectors, each of which isconfigured for receiving said locating signal; b) locating saiddetectors at initial positions in said region within range of saidelectromagnetic locating signal transmitted from the boring tool at itsinitial position; c) providing a transmitter arrangement forming onepart of at least a first one of said detectors for transmitting arelative locating signal to other detectors in a setup mode; d)receiving said relative locating signal using a second one of saiddetectors in said setup mode; and e) determining the position of thesecond detector relative to the first detector based on the receivedrelative locating signal.
 18. The method according to claim 17 furthercomprising: e) receiving said electromagnetic locating signal in apredetermined way using said first and second detectors to produceelectromagnetic data; and f) establishing initial absolute positions ofsaid detectors and said boring tool within said region using certaininformation including the electromagnetic data in conjunction with therelative position established between the detectors.
 19. The methodaccording to claim 18 wherein said detectors include tilt sensors formeasuring the tilt angles of each detector such that the tilt angles ofeach detector form part of said certain information.
 20. The methodaccording to claim 18 wherein receiving the electromagnetic locatingsignal in said predetermined way includes: measuring saidelectromagnetic locating signal using the detectors with the boring toolat its first, initial position to produce a first subset of saidelectromagnetic data, moving the boring tool to a second position anddetermining a distance between the first and second positions, measuringthe electromagnetic locating signal with said boring tool at the secondposition to produce a second subset of said electromagnetic data, andwherein determining the initial absolute positions of the detectors andthe boring tool within said region includes combining the first andsecond subsets of electromagnetic data to produce the overallelectromagnetic data, and determining the absolute positions of thedetectors and the boring tool in said region using the overallelectromagnetic data in conjunction with the established relativeposition between the detectors.
 21. The method according to claim 18wherein said system includes a drill rig having an extendable drillstring attached to said boring tool such that movement of the boringtool is accomplished by extending or retracting the drill string andwherein receiving the electromagnetic locating signal in saidpredetermined way includes: measuring said electromagnetic locatingsignal using the detectors with the boring tool at its first, initialposition to produce a first subset of said electromagnetic data, movingthe boring tool to a second position and determining a distance betweenthe first and second positions, measuring the electromagnetic locatingsignal with said boring tool at the second position to produce a secondsubset of said electromagnetic data, and wherein determining the initialabsolute positions of the detectors and the boring tool within saidregion includes combining the first and second subsets ofelectromagnetic data to produce the overall electromagnetic data, anddetermining the absolute positions of the detectors and the boring toolin said region using the overall electromagnetic data, along with theestablished relative position between the detectors and said distancemeasured between the first and second positions of the boring tool, indetermining the absolute positions of the detectors in said region. 22.The method according to claim 21 wherein receiving said electromagneticlocating signal in said predetermined way further includes producing oneor more additional subsets of said electromagnetic data at one or moreadditional positions of said boring tool, said additional subsets ofelectromagnetic data, thereafter, being used in said absolute positiondetermining as part of the overall electromagnetic data in a way whichimproves accuracy in determining the absolute positions of the detectorsand the boring tool in said region.